In recent years, in order to solve environmental and energy problems, various electric cars have been expected to be widespread. As the on-vehicle power source such as a motor drive power source that is crucial for practical application of these electric cars, development of secondary batteries has been actively conducted. However, in order to attain widespread use, it is required to allow batteries to have high performance and to be more inexpensive. Further, as for electric cars, they are required to have a mileage per charge that is closer to gasoline engine powered cars. Under such circumstances, a battery having higher energy has been awaited.
In order to allow a battery to have a high energy density, an amount of electricity stored per unit mass of each of a positive electrode and a negative electrode is required to be large. As the positive electrode material that may be able to meet such a request, a so-called solid-solution positive electrode has been studied (for example, Patent Document 1).